Considering Gram is dealing overwhelmingly slash damage as base I thought Buzz Kill’s +120% slash damage would be a slam dunk on it, yet none of the popular builds use that mod.
Does this have something to do with how damage is calculated that I’m missing or are physical damage increase mods just always a bad idea?
Usually because unless you are trying to get a certain status proc, physical damage mods kinda suck. Since a slash mod will adjust according to the BASE SLASH damage of the weapon, while elemental mods damage increase is based on all of the base damage of the weapon.